Wireless communication systems may be based on Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA) or some other multiple access schemes. A CDMA-based wireless network may implement one or more standards such as 3GPP2 IS-2000 (commonly referred to as CDMA 1x), 3GPP2 IS-856 (commonly referred to as CDMA 1xEV-DO), and 3SGPP UMTS (Universal Mobile Telecommunications System) A TDMA/FDMA-based wireless network may implement one or more standards such as 3GPP Global System for Mobile Communications (GSM). 3GPP General Packet Radio Service (GPRS) is an extension of GSM to provide packet data service. A radio access technology (RAT) indicates the type of radio technology to access the associated wireless core network. Examples of RATs include CDMA 1x or CDMA 1xEV-DO (collectively referred to as CDMA from hereafter), GSM, and UMTS. A CDMA core wireless network may include a Mobile Switching Centre (MSC), a Home Location Register (HLR), an Access Authorization and Accounting (AAA) Server, a Home Agent (HA) and a Foreign Agent (FA). A GSM core wireless network may include a Mobile Switching Centre (MSC), a Home Location Register (HLR), a Serving GPRS Support Node (SGSN) and a Gateway GPRS Support Node GGSN.
Each of the systems is used to provide wireless radio coverage in a given geographical area as defined by the wireless network operators who own the radio spectrum and the access technology. In some areas, only one radio access technology is available. In other areas, multiple radio access technologies are available. To allow for more comprehensive roaming, mobile devices have been implemented that support multiple RATs.
A mobile device supporting both GSM and CDMA faces a number of challenges in terms of scanning, acquisition, and selection of a proper wireless network of a given RAT. Multiple RAT acquisition cannot take place simultaneously on a mobile device that has a single receiver. It becomes even more challenging if the device is to provide a “global” wireless network scan mode that automatically selects a RAT (CDMA or GSM) that provides preferred service (based on primary services expected of the mobile device) without any user intervention. Main factors behind these problems are summarized below.
To acquire a CDMA wireless network, mobile device uses an operator-provided list called Preferred Roaming List (PRL) that controls the CDMA systems that the mobile device can acquire as well as the priority order associated with each system. Similarly, GSM system acquisition is controlled by operator provided Public Land Mobile Network (PLMN) list that resides in the Subscriber Identity Module (SIM). Currently, no mechanism exists to combine network information associated with CDMA and GSM. In other word, the PRL used for CDMA scanning and the PLMN list used for GSM scanning are quite disjoint. As a result, the mobile device has no a-priori knowledge of whether there is a GSM/CDMA overlay in a given geographical area and whether the mobile device can acquire services using either of GSM and CDMA or both.
Roaming agreements between a home wireless network operator and its roaming partners do not necessarily converge on using the same RAT due a variety of reasons which can be broadly categorised as financial (e.g. cost of roaming, revenue sharing) or technical (lack of same RAT support). A CDMA carrier “X”, may have both voice and data roaming agreement with another CDMA wireless network operator “Y” in country “A”. However, same CDMA carrier “X” may have only voice roaming with CDMA wireless network operators in country “B” whereas it may have both voice and data roaming with a GSM carrier “Z” in country “B”. In country “C”, there may not be any systems that use CDMA—as a result, the viable option for roaming device from operator “X” is to use GSM service provided that “X” has roaming agreement with a GSM operator in country “C”. In addition, roaming based on business agreements and as a result subject to change at any time.